Outline

Objective: The corticospinal tract is in proximity of the classical targets for Deep Brain Stimulation (e.g. STN, VIM and GPi). Stimulation of the tract causes side effects that interfere with the therapeutic effect of stimulation. Therefore an accurate visualisation of this anatomical structure might enhance the preoperative planning and intraoperative localisation of the optimal electrode positioning. The goal of this study was to correlate the distance of the corticospinal tract displayed on navigated transcranial magnetic stimulation-based tractography to the finally implanted electrode contacts with the threshold in motor evoked potentials (MEP).

Methods: 11 patients with 21 electrodes were analysed in this study (STN = 5, VIM = 5 and GPi = 1). The motor cortex was assessed by navigated transcranial magnetic stimulation in 9 out 11 patients and according to the classical landmarks in two out of 11 patients. Tractography was performed with diffusion tensor imaging (DTI) on a 3 Tesla scanner with 64 diffusion directions. The DTI Sequences were coregistered with the preoperative planning MR and the pre- and postoperative stereotactic CCT. Intraoperatively MEP thresholds were assessed by stimulation of the final DBS electrode. The distance of the minimal distance of the stimulated electrode contact and the pyramidal tract was measured by calculating the vector error.

Results: The mean minimal distances of the stimulation contacts to the pyramidal tract on DTI was 4,1mm (0,3–9,7 mm). The mean stimulation threshold was 5,22 mm. The result of the Pearson correlation was a correlation coefficient of 0,83 and p = 0,001.

Conclusions: The pyramidal tract as demonstrated on DTI seems to have a highly significant linear correlation to the motor threshold during intraoperative motor evoked potentials. Optimal distances have to be assessed for every target area individually in a greater number of patients. This might be another step towards DTI-guided deep brain stimulation.